Have roommates? Don't adjust the temperature in the shower! Need we get in a cycle, every day, struggling for almost a whole minute to get just the right heat, only for our work to be undone later that same day, and redone tomorrow?
I think habits of small kindnesses can make the difference between a good world and a great one. Let's think of more of these together.
Do the math for yourself, but I've started leaving nickels in the take a penny leave a penny thing along with all my pennies. Part of this is my insistence pennies and nickels are wastes of time, but it also makes life easier for someone else. I might even start leaving dimes, considering how rarely I use cash – at low frequency, it costs less, and means you're lugging around change for longer.
Now, I've never bumped into someone noticeably failing on this score, but I've also never seen this written down as etiquette, so: wash your plunger after every use. It is probably being used in a room with a shower, so a high pressure blast is but a moment away.
If a phone setting can eliminate an entire Curb Your Enthusiasm episode's worth of social confusion, are we obligated to use that system? I don't know for sure, but I will say that every single human should use the Do Not Disturb setting on their phone to enforce their call/text cutoff (this is the focus on a recurring joke in a very early Curb episode). Everyone has been called too late for comfort. Everyone has been woken up by a text. This is solvable now, and I'm loving it.
If you've ever had something you love to share with someone, do a culture swap with them. Say, "I'll watch the first season of Arrow if you watch the first season of Billions". But, what if, for instance, my younger brother still hasn't watched Billions, but I watched every bland minute of Arrow's Season 1 – what then? Maybe watch more things with people. Excepting exceptionally awkward family-time experiences (like Game of Thrones), most things you truly enjoy should be shared with people you care about. And we should focus our live more on things we like so much we wouldn't mind sharing them in person.
Keep a notebook of when people are nice to you. It would be a shame if you didn't even notice, and yet, many people do not. Build a system so you do, and remember to return kindness twice over, for all the times you don't see.